Anchoring member

Abstract

An anchoring member for connecting a rod with a bone comprises a screw member having a treaded portion and a screw head with a spherical segment-shaped portion, a seat part receiving said screw head of said screw member and said rod, and a pressure member formed to embrace said screw head from its side opposite to said threaded portion. The seat part has a first end, a second end opposite to said first end, an axis of symmetry passing through said first and second end and a bore which is coaxial with said axis of symmetry for passing said threaded portion therethrough and has a first portion adjacent to said first end, said first portion having a substantially U-shaped cross-section with two free legs with an internal screw thread for receiving said rod therebetween. The seat part further has a second portion adjacent to said second end, said second portion tapering towards the second end with a predetermined cone angle, and a pressure member has an outer conical surface in a region laterally surrounding said screw head, said conical surface tapering towards said second end with a cone angle corresponding to said predetermined cone angle.

What is claimed is: 
     
       1. An anchoring member for connecting a rod with a bone, said anchoring member comprising a screw member having a threaded portion and a screw head with a spherical segment-shaped portion,   a seat part receiving said screw head and said rod, said seat part having a first end, a second end opposite to said first end, an axis of symmetry passing through said first and second ends, a bore which is coaxial with said axis of symmetry for passing said threaded portion therethrough and has a first portion adjacent to said first end, said first portion having a substantially U-shaped cross-section with two free legs with an internal screw thread for receiving said rod therebetween, and a second portion adjacent to said second end, said second portion tapering towards said second end with a predetermined cone angle,   and a pressure member formed to embrace said screw head from its side opposite to said threaded portion and having an outer conical surface in a region laterally surrounding said screw head, said conical surface tapering towards said second end with a cone angle corresponding to said predetermined cone angle.   
     
     
       2. The anchoring member of claim 1, said predetermined cone angle being in the range of from about 2° to approximately 10°. 
     
     
       3. The anchoring member of claim 1, the cone angle being about 4°. 
     
     
       4. The anchoring member of claim 1, wherein said pressure member has a first face and an opposite second face, a substantially cylindrical first portion adjacent to said first face having an outer diameter sized for a sliding fit of said pressure member within said bore, and a second portion adjacent to said first portion, said second portion being formed as a trancated cone having an outer surface which conically tapers towards said second face. 
     
     
       5. The anchoring member of claim 4, comprising a first recess formed within said second portion of said pressure member for receiving said screw head, said first recess being shaped as a spherical segment and opening towards said second face. 
     
     
       6. The anchoring member of claim 5, comprising a bore formed in said pressure member for passing a screwing tool therethrough into engagement with said screw head, said bore being coaxial with a cylinder axis of said first portion and joining said first recess. 
     
     
       7. The anchoring member of claim 5, comprising a plurality of longitudinal slits formed in said pressure member, said slits having a longitudinal axis extending parallel to the axis of said first portion and being open towards said second face. 
     
     
       8. The anchoring member of claim 7, comprising two opposite longitudinal slits each having a longitudinal axis, the two longitudinal axes lying in a plane passing through the cylinder axis of said first cylindrical portion and extending perpendicular to said cylinder axis of said second recess, said longitudinal slits extending closely to said first face of said pressure member. 
     
     
       9. The anchoring member according to claim 5, wherein said first recess has a depth in axial direction and a radius, said depth being greater than said radius. 
     
     
       10. The anchoring member of claim 1, comprising a second recess formed in said pressure member on the side thereof opposite to said screw head, said second recess having the shape of a cylinder portion with an axis extending perpendicular to said axis of symmetry and having a radius of a curvature which corresponds to a radius of curvature formed at a base of said U-shaped first portion defined by said two legs.   
     
     
       11. The anchoring member of claim 1, comprising crimp means for securing said pressure member with said screw head therein against rotation within said seat part. 
     
     
       12. The anchoring member of claim 1, comprising a swivel nut member embracing said two free legs on the outside thereof, said legs having an external screw thread and said swivel nut member having an internal screw thread cooperating with said external screw thread, and a locking member for locking said swivel nut member, said locking member having an external screw thread and said legs having an internal screw thread engaging said external screw thread of said locking member.